Flexible thermoplastic resins as binders for vulcanized rubber



United States Patent Oflice 3,489,710 Patented Jan. 13, 1970 US. Cl. 26033.6 13 Claims ABSTRACT OF THE DISCLOSURE Interpolymers of ethylene with copolymerizable olefinically unsaturated monomers and post-reacted ethylene homopolymers having tensile strengths above 500 p.s.i., tensile elongations above 200 percent and torsional rigidity between about 2000 and 15,000 p.s.i. are shown to be highly compatible binders for vulcanized rubber scrap and rubber dust.

This invention relates to a reconstituted rubber product which is formed by bonding together vulcanized rubber scrap particles and vulcanized rubber dust.

Vulcanized rubber scrap and vulcanized rubber dust are created whenever rubber products, or products utilizing rubber components, are subjected to manufacturing processes. Rubber scrap and rubber dust result from the many trimming, finishing, and polishing operations that are carried on throughout industry. The usual practice in industry is to dispose of this rubber scrap and rubber dust as waste. Hence, hundreds of tons of this scrap material are either burned or discarded each year while only small amounts are incorporated in low quality grade mechanical rubber goods.

Until recently, there has been no way in which this waste material could be used in the versatile manner which this invention discloses so that it would be of economic value and importance. Attempts to employ conventional thermoplastic polymers such as polyethylene as a binder for bonding vulcanized rubber scrap particles have not been successful. The resultant products are unsatisfactory since they are quite rigid, are very low in elongation, and have such low flex-crack resistance as to appear brittle. These deficiencies become even more pronounced when a polyethylene binder is employed in attempting to compound compositions having a high rubber content.

In like manner, vulcanizable rubber formulations, such as a butadiene-styrene rubber, butyl rubber and the like, have been attempted as binders for bonding vulcanized rubber scrap particles. The resulting products are also quite unsatisfactory since they exhibit very low tensile strengths. While vulcanizable rubber binders reinforced with carbon yielded improved products, they still exhibit poor elongation, even at very low modulus and are, therefore, equally unsatisfactory.

It is an object of this invention, therefore, to obtain a reconstituted rubber product wherein particles of vulcanized rubber scrap and vulcanized rubber dust are bonded together through the use of selected, flexible, thermoplastic resins.

It is a further object of this invention to obtain reconstituted rubber products which exhibit significantly improved and superior mechanical properties.

Another object of this invention is to obtain reconstituted rubber products which contain between 40-90% by weight vulcanized rubber scrap and vulcanized rubber dust particles.

These and further objects of this invention will, in part, be obvious and will, in part, be made more clear from the ensuing discussion.

It has recently been discovered that significant quantities of waste vulcanized rubber scrap and vulcanized rubber dust in amounts as high as %-90% by weight can now be bonded together and a product obtained which exhibits surprisingly superior properties than has been heretofore attainable.

Thus, it is now possible to obtain reconstituted rubber products which exhibit such superior properties as greater tensile strength, a higher percentage of elongation, significantly more flexibility and noticeably improved flexcrack resistance than has been heretofore attainable.

The reconstituted rubber products having these superior properties are obtained through the use of specific, flexible, thermoplastic resins acting as the bonding agents.

Further, it has also been found that, through the use of these selective resins acting as bonding agents, a significantly greater amount of vulcanized rubber scrap particles and vulcanized rubber dust particles may be bonded together than has been heretofore realizable. Formerly, it has only been possible to obtain a product comprised of between about l030% by weight rubber scrap and rubber dust particles. Now, however, by employing the selected, flexible, thermoplastic resins as discussed hereinbelow, it is possible to obtain desirable and functional products which contain as much as or more, by weight vulcanized rubber scrap and vulcanized rubber dust particles for use as shoe soles, heels and other similar uses.

By the term, reconstituted rubber is meant that product which is formed from the practice of this invention and is the result of bonding together vulcanized rubber scrap particles and vulcanized rubber dust with selected thermoplastic resins. Hence, all reference throughout this application to the term reconstituted rubber will be understood to mean and refer to the definition just stated.

The bonding agents that are used as binders in the practice of this invention are selected from the group of resins generally designated as flexible ethylene polymers. This group of polymers is relatively new, having only recently become commercially available within the past 3-4 years. This group includes such polymers as ethylene intenpolymers with, for example, copolymerizable olefinically unsaturated monomers as acrylic acid, alkyl acrylates, vinyl acetate, propylene, butene, bicycloheptene, methyl ethyl vinyl acetamide and so forth, as well as post-reacted ethylene homopolymers; for example, those which are chlorinated, chlorosulfonated, and so forth, in order that elastomeric properties may be imparted to the ethylene-based polymers.

Terpolymers have also been found to be efficient binders; particularly those which contain reactive groups in their molecular structure such as the carboxyl and hydroxyl groups, or residual unsaturation, as in the ethylenepropylene-diene terpolymers.

More particularly, the flexible binders employed in the practice of this invention are those which exhibit specific mechanical properties; that is, wherein the polymer, without vulcanization has a tensile strength of more than 500 p.s.i., a tensile elongation of more than 200 percent, and a torsional rigidity of more than 2000 p.s.i. Preferably, the thermoplastic polymers should exhibit mechanical properties wherein tensile strength is more than 1000 p.s.i., tensile elongation is greater than 500 percent and the torsional rigidity is higher than 2000 p.s.i. but less than 15,000 p.s.i.

It will be readily apparent to those skilled in the art that the various groups of polymers, described hereinabove, which may be used as binders contain completely different chemical properties. Nevertheless, the correct flexible, thermoplastic polymer can be selected from these chemically dissimilar polymers to form the reconstituted rubber products of the instant invention when the thermoplastic polymers described hereinabove exhibit mechanical properties of tensile strength greater than 500 p.s.i., tensile elongation of more than 200 percent and torsional rigidity of at least 2000 psi. lbut less than 15,000 psi.

The vulcanized rubber scrap and vulcanized rubber dust utilized in the practice of this invention is obtained from the scrap of various product manufacturing processes; such as, automobile tires, heels for shoes, weather proofing strips, and so forth. This type of rubber scrap is usually flexible and non-flowing. Generally, the composition of this rubber scrap includes such ingredients as clay fillers, carbon black, silicas, modifiers, extenders, and so forth. Typically, the formulations of these rubber products include not only the various grades of natural rubber, but also synthetic rubbery polymers, as is exemplified by styrene-butadiene copolymer rubbers and related 'butadiene polymers; such as, polybutadiene, polychloroprene, polyisobutylene, polyisopropene, and the nitrile polymers; such as acrylonitrilebutadiene copolymers, the acrylonitrile-styrene-butadiene terpolymers and like materials, the olefin rubbers; such as, the ethylene-propylene copolymers and ethylene-propylene-diene terpolymers and like rubbery polymers that have been vulcanized by agents to yield tough, elastomeric, thermally stable vulcanized rubber products whether they are vulcanized with sulfur or sulfurcontaining vulcanization agents; or other agents such as organic peroxides, isocyanates, metal oxides, or other cross-linking agents, or with mixtures of several such crosslinking vulcanization agents. In short, all the various vulcanized or cross-linked rubber formulations and composi tions commonly known to and used by those skilled in the industry can be employed in this invention.

Hence, while a wide variety of vulcanized rubber scrap and vulcanized rubber dust may be used, that which is obtained as waste from the manufacture of rubber tires and rubber heels for shoes is preferred and is most readily available in large quantities.

Depending upon the nature and type of end product desired, the amount of finely divided rubber scrap particles to be formulated with the thermoplastic polymer may vary between about 20:1 to 05:1 parts by weight of rubber to polymer, respectively, and, preferably, between about :1 to 1:1 parts by weight of rubber to polymer, respectively.

Generally, an increase in the amount of polymer incorporated will result in end products which have smoother surfaces and greater flexibility. Conversely, incorporation of greater amounts of vulcanized rubber particles will result in stifier end products having less flexibility and rougher surfaces.

The flexible thermoplastic polymers, or compositions, selected for use as bonding agents may also be cross-linked through the utilization of proper cross-linking agents. When interpolymers are used, for example, peroxidic-type cross-linking agents, such as dicumyl peroxide, benzoyl peroxide, and so forth, are extremely useful. Usually a cross-linking agent of the peroxide type is incorporated into the mix at temperatures below which the peroxide radical will decompose.

Where polymers containing reactive sites, such as residual unsaturation, hydroxyl or carboxyl groups, are selected for use as bonding agents, then suitable cross-linking agents may be used such as sulfur, isocyanates and so forth. These binders may be preferred particularly where the inherent odor resulting from the use of peroxide crosslinking agents is offensive.

The cross-linking agents discussed hereinabove are representative of those commonly used in industry to obtain cross-linking and are well known to those skilled in the art.

It may also be desirable to produce a product which has greater flexibility, particularly where the bonding agents are to be cross-linked. Greater flexibility may be obtained by incorporating suitable plasticizers into the composition. Among the plasticizers which may be used to attain greater flexibility are those which fall into the general class of mineral extender oils. Typical of the mineral extender oils which may be employed and which are commercially available, are the highly aromatic extender oils containing about 30 percent aromatic carbons and having a viscosity of 93 SSU at 210 F. In like manner, typical naphthenic extender oils containing about 42 percent naphthenic carbons and having a viscosity of 40 SSU at 210 F. may also be used. In addition to these, plasticizers such as dioctyl phthalate may also be used. These plasticizers are representative of those generally employed in the plastics industry and their application is Well known to those skilled in the art.

Whenever plasticizers are used, they may be incorpo rated into the composition in amounts of, depending upon the compatibility of the plasticizer, preferably up to about 5 percent by weight. This amount appears to be optimum. When employed in the instant invention the amount of plasticizer incorporated was calculated from the total weight of the mixture consisting of the vulcanized rubber scrap particles and the flexible thermoplastic polymer.

Generally, the reconstituted rubber products of the in stant invention may be manufactured by a typical processing method such as is outlined below:

(1) Vulcanized rubber scrap and vulcanized rubber dust are ground to particle size of between about 20 and mesh.

(2) To these particles is added a specifically selected, flexible thermoplastic polymer.

(3) This composition is then milled in a standard milling machine, such as a Banbury mill.

(4) The resulting composition may then be molded, extruded, calendered and so forth to form the final reconsituted rubber product desired.

If the polymer or composition is to be cross-linked, a s(ui)table cross-linking agent is usually added before step Where plasticizers are desired, they may be added before the mixture is milled.

In forming an end product from the reconstituted rub ber, various processes may be utilized depending upon the nature and type of product desired. For example, the reconstituted rubber formed may be calendered, extruded, compression molded, injection molded, sintered and fused, mold casted, foamed and so forth in accordance with methods well known in the art.

Whenever a calendering process is used, it may be desirable to use releasing agents, such as, zinc stearate, in order to facilitate removal of the composition from the calendering rolls.

Compounding the vulcanized rubber scrap may be achieved through typical processes whereby the scrap rubber is formed into powders, granules or particles of varying size and shape and so forth.

It should be understood that products containing different surface compositions and textural appearances may also be obtained where desired by using particles of relatively larger size than the 20150 mesh size indicated above. Use of larger particles would be of particular interest where the end particles is to be decorative as well as functional. For example, in the manufacture of floor tiles and ceiling and wall panelings, larger particles of vulcanized rubber scrap may be utilized to create a decorative' effect in these functional products. Such products are readily obtainable by placing relatively large particles of vulcanized rubber scrap in the order of about to in thickness, ,4" to in width, and to 2%" in length in the Banbury, milling at elevated temperatures and then adding to the partially ground batch the specifically selected thermoplastic polymer. The size of these relatively large particles of vulcanized rubber scrap may be varied so that there is created in the final product the effect of chips, nuggets, and so forth.

When such larger particles are used, the final product will tend to have a more heterogeneous appearance as opposed to the homogeneous effect created by incorporating particle sizes of 20-150 mesh. However, it should also be understood that larger particles, such as those described non-vulcanized copolymer per se employed in each of the aforementioned examples as illustrated and defined in Example I above.

immediately above, may be blended with smaller particles 5 EXAMPLE H of 20-150 mesh to create a still further decorative effect. The Same Procedure was tehowed as'lh Example I In like manner, these particles may also vary in color P that a P y y having a density of and a when Such an ff t is desired melt index of 1.5 was used in place of the ethylene-ethyl It is readily apparent, therefore, that a wide variety of acrylate p lf The control listed hhder Example reconstituted rubber products maybe obtained by utiliz- 10 H Table I 18,.thefet0re, the ahove-ldehtlfied ing standard equipment and process methods. Among the eahlled h y y many products that may be obtained are such items as lRetemhg to Table 1t 13 pp that the P q rug backings for non-skid rugs or mats, trunk linings for ohtalheft w the Polyethylene of Example H'WflS used automobiles, floor mats, roofing, weather stripping, sealhas a slgnlficantly lower Percentage of elohgahoh h a ing gaskets, inner linings for shoes, shoe soles, shoe heels, 15 much hlghel' Stiffness modulus h h the P q ehtalhed decorative Wall or ceiling absorbing panels, toys, electrifrom E p Further, the lhltlal tear strength and cal insulation, blowmolded bottles, injection moldings, final failure, as determlned by the Ross Rubber Flex Test, coatings, laminates and so forth. occur after noticeably fewer cycles.

By way of illustration, the following examples are set These dlfierehces P h' and mechahlcal forth as being merely exemplary and not limitative, of the Propeftles of the p q es tamed are equally apparent manner in which vulcanized rubber scrap particles and e Compared to the test results Of the other examples vulcanized rubber dust particles may be bonded with a as hsted Table selected thermoplastic polymer to form the new recon- EXAMPLE HI stituted rubber product of this invention. All percentages h same procedure was followed as in Example I, are in PartS y Weightexcept that an ethylene-propylene copolymer, containing 36 percent of combined propylene and having a melt in- EXAMPLE I dex of 0.1, was used in place of the ethylene-ethyl 80 grams of vulcanized rubber scrap and vulcanized acrylate copolymer. The control is the above-identified rubber dust, having a particle size of about 35 mesh, were non-vulcanized ethylene-propylene copolymer. milled with 20 rams of an ethylene-eth l acrylate copolymer, containing about 15 percent combiiied ethyl acrylate EXAMPLE 1V and hag/ing a melt index of 6.0, on a two roll rubber mill The Same procedure was followed as in Example I, at 105 for 4 minutes. The resultant compoun was except that an ethylene-bicycloheptene, containing 17 corhpressloh molded at uhder a pressurehf ercent combined bicycloheptene and having a melt index p s.1. to yreld a reconstltuted rubber plaque measurlng of 7.5, was used in place of the ethylene-ethyl acrylate 6 X 6 X Plaque was 21 9? to Standard copolymer. The control is the above-identified non-vultests to measure tensile strength, flexibility and percent canized ethyknebicyclohcptene copolymen elongation. The test methods used to measure tensile strength and percent elongation were conducted accord- EXAMPLE V ing to ASTMD63858T. The test method used to meas- 40 ure flexibility was conducted according to ASTM-D-747- The Same procedure W followed as m EXample.I 58T- except that an ethylene-vinyl acetate copolymer contam- The plaque was also tested to measure flex life. This i Percent combined Y acetate and havmg a melt test was conducted according to the Ross Rubber Flex Index of was placi the ethylfme'efhyl Test method. The ROSS Rubber Flex Life Test employs a acrylate copolymer. The control 1s the above-identlfied specimen measuring X having a thickness of 125 non-vulcanized ethylene-vinyl acetate copolymer. mils. The specimen is bent through a 90 arc at a rate of 100 times per minute. When desired, a slit measuring 100 EXAMPLE VI mils in width may be cut in the specimen to obtain a con- The ame procedure was followed as in Example I, trolled flaw. When no slit is employed, the results are reexcept th t a hlo i t d polyethylene copolymer was ported as the number of cycles required to obtain initial used in place of the ethylene-ethyl acrylate copolymer, cracking or total failure. When the controlled flaw is used, which contained 20 percent chlorine and had a density of the results are reported as the increase in length of the 0.92, a melt index of 2.0, and which was stabilized with slit after the specimen is subjected to a given number of 3,0 percent of a dibasic lead phosphite having the gen- CYCIeS (Ca y, R- H., ASTM Bulletin No. 206, 1955). eral formula ZPbOPbHPO -LZH O. The control is The results obtained from these tests were compared the above-identified non-vulcanized chlorinated polyto the mechanical properties of same copolymer per se; ethylene copolymer. that is, the non-vulcanized ethylene-ethyl acrylate copoly- Examples I-VI above serve to illustrate that use of mer. These results are tabulated in Table I wherein the a selected thermoplastic polymer whose mechanical propcopolymer properties are listed as control. erties exhibit a tensile strength in excess of 1000 p.s.i., a Table I also lists, in a similar manner, the test results tensile elongation of over 500 percent and a torsional for the products obtained in Examples II-VI which folrigidity of between about 2,000 and 15,000 psi. will low. The term control is intended to apply, in each in yield excellent reconstituted rubber products securing stance, to the mechanical properties of the corresponding product properties such as those listed in Table I.

TABLE I Example I Example II Example III Example IV Example V Example VI Control Plaque Control Plaque Control Plaque Control Plaque Control Plaque Control Plaque Tensile Strength, p.s.i 1,400 750 1,800 800 700 400 2, 000 800 1,100 650 1,160 585 Percent Elongation 700 130 00 40 500 200 700 280 705 60 Flexural Stiffness at 23 0.,

p.s.i 5,000 5,100 18,000 9,000 2,200 4,000 9,200 5,000 3, 000 3,900 3,500 3, 520 Ross Rubber Flex Life,

gi liial Tear 20,000 9,000 450 25 100 250 500,000+ 415 Final Failureun 500, 000 70,000 30, 000 000 7,000 3,500 o) 500, 000+ 7,000

' Not measured.

In order to further illustrate the use of ethylene polymers and modified ethylene copolymers as binders in the instant invention, two different plasticized vinyls were selected and used as binders. One plasticized vinyl was selected which had a flexural stiffness nearly equivalent to the ethylene-ethyl acrylate copolymer while the other plasticized vinyl had a flexural stiifness substantially lower than the ethylene-ethyl acrylate copolymer. The products obtained from using the plasticized vinyls were also compared with vulcanized rubber products wherein styrene butadiene and butyl rubber formulations were employed. The manner in which these products were obtained is set forth in Examples VII-XI below. The results obtained from subjecting the products of Examples VlI-XI to the same tests as were conducted for Examples I-VI above are set forth in Table II.

8 EXAMPLE X The same procedure was followed as in Example VII except that parts of a vulcanizable butadiene-styrene rubber was used in place of the plasticized polyvinyl chloride of Example VII. The butadiene-styrene rubber formulation was comprised of 1500 parts of butadienestyrene rubber, containing 23.5% combined styrene and 76.5% butadiene, 750 parts of carbon black, 2.0 parts sulfur, 1.25 parts of a benzothiazyl disuliide cumate and 0.25 part of a synthetic resin mixture of polymerized coumarone, indene and homologous compounds. The butadiene-styrene rubber composition cured in 20 minutes at 310 F.

The results obtained are set forth under Example X of Table '11.

TABLE II Example VII Example VIII Example IX Example X Example XI Control Product Control Product Product Product Product Control Tensile Strength, p.s.i 3, 300 2, 200 600 750 370 130 Percent of Elongation 210 260 15 65 95 140 Flexural Stiffness, p.s.i 4, 200 910 7, 300 1, 910 1, 370 156 Flex Life, Ross Rubber Method, cycles:

Initial Tear 20 232 16, 000

Final Failure 500, 000 2, 000 250, 000 200, 000

1 Too brittle and weak to test.

2 Not capable of testing; product was too weak and deformed easily.

a Not measured.

EXAMPLE XI EXAMPLE VII 20 parts of a plasticized polyvinyl chloride having a flexural stiffness equivalent to the acrylate copolymer of Example I above was compounded with 80 parts of vulcanized rubber dust having a particle size of about 35 mesh. The process employed was the same as that which is set forth in Example I above. The polyvinyl chloride was comprised of 71.8 parts of a polymerized suspension of polyvinyl chloride, 26.6 parts of dioctyl phthalate, 0.7 part of a liquid barium-cadmium stabilizer, 0.4 part of an organic phosphite stabilizer, 0.8 part of a liquid epoxy stabilizer and 0.3 part stearic acid.

The resulting product was subjected to the same tests employed for the products of Examples I-VI above. In like manner, the mechanical properties of the aboveidentified plasticized polyvinyl chloride per se were taken as a measuring control. The results obtained are set forth in Table II below wherein control is intended to identify the plasticized polyvinyl chloride per se.

EXAMPLE VIII The same procedure was followed as in Example VII except that 20 parts of a plasticized polyvinyl chloride having a lower flexural stiffness than the acrylate copolymer of Example I above was used instead of the plasticized polyvinyl chloride of Example VIII. This plasticized vinyl was comprised of 62.9 parts of a polymerized suspension of a polyvinyl chloride, 35.0 parts of dioctylphthalate, 0.6 part of a liquid barium-cadmium stabilizer, 0.4 part of an organic phosphite stabilizer, 0.8 part of a liquid epoxy stabilizer and 0.3 part stearic acid.

The control listed under Example VIII of Table II is, therefore, the above-identified plasticized polyvinyl chloride.

EXAMPLE IX The same procedure was followed as in Example VII except that 20 parts of a vulcanizable butyl rubber was used in place of the plasticized polyvinyl chloride of Example VII. The butyl rubber formulation was comprised of 1500 parts polyisobutylene rubber modified with about 290 isoprene, 750 parts of carbon black, 75 parts zinc oxide, 15 parts stearic acid, 75 parts of a chlorosulfonated polyethylene synthetic rubber, containing about 29% chlorine and 1.2% sulfur, 3.0 parts sulfur and 1.0 part methyl. The butyl rubber composition cured in 15 minutes at 175 C.

The same procedure was followed as in Example VII except that a vulcanizable butadiene-styrene rubber, not reinforced with carbon black, was used in place of the plasticized polyvinyl chloride of Example VII. This butadiene-styrene rubber formulation was comprised of parts of a but-adiene-styrene rubber containing 23.5% combined styrene and 76.5% butadiene, 2.5 parts sulfur, 1.25 parts of a benzo-thiazyl disulfide cumate and 0.25 part of a synthetic resin mixture of polymerized coumarone, indene and homologous compounds. This composition cured in 20 minutes at 310 F.

A comparison of the results listed in Tables I and II reveals that ethylene polymers and modified ethylene copolymers having lower crystallinity can be employed as effective binders for vulcanized rubber scrap particles and vulcanized rubber dust particles.

It can be seen that mechanically, the ethylene polymer and its modified copolymers display similar qualitative performances with the exception of the polyethylene having a flexural stiffness of 18,000 (Table I, Example II) which yielded products which were found to be significantly more rigid and were prone to cracking upon flexing. This precludes their use for obtaining the flexible products which are obtainable when copolymers having a lower flexural stiffness are employed.

On the other hand, if the copolymers have a flexural stiffness which is too low, they become weak and begin to display the low tensile properties of the non-reinforced vulcanized rubber compositions. For example, compare Example III of Table I with Example XI of Table II. Furthermore, the type of substituent in the ethylene polymer does not appear to be as important as the mechanical properties that result from the introduction of a comonomer unit. Hence, excellent results are obtainable when the selected thermoplastic polymer used as the binder has the optimum mechanical properties of tensile strength of more than 500 p.s.i., a tensile elongation of over 200%, and a torsional rigidity of at least 2000 psi, but less than 15,000 psi.

It follows, therefore, that a large number of modified ethylene polymers can be utilized as binders in this invention and perform substantially as well as the flexible ethylene polymers employed herein.

With regard to the plasticized polyvinyl chloride compositions, it was found (from Tables I and II) that those having a flexural stiffness similar to the acrylate copolymer yielded products which crumbled (Table II, Example 9 VII). On the other hand, the plasticized polyvinyl chloride containing a higher plasticizer content (Table II, Example VIII) yielded products having low elongation and poor flex-crack resistance. Furthermore, this composition became highly brittle when heat-aged in an oven at 80 C.

It will be readily apparent to those skilled in the art that removal of the hot plaque without first cooling the mold substantiates that cross-linking did, in fact, occur since this ability to remove the hot plaque from a hot mold is characteristic of a vulcanized rubber product. If

for 15 days, while those compositions wherein the acrylcrosslinking h d t t k l h plaque ld h ate copolymer was used remained unchanged when subh d a h -lik consistency and would not h jected to the same heat-aging test. tained its molded shape.

when conlpafed t0 PIaStiCiZe-d P y y chlorides F Additional examples illustrating the use of other use as bmders, the selected thermoplastlc resins whlch selected thermoplastic cross-linkable copolymers are set P -Y T116 Optimum mechanical prope tie Set forth forth below. As in all the preceding examples, the folhereinabove are distinctly advantageous in that y lowing examples are intended as merely being exemplary Veal n0 Plasticilef migration or embfitflelnent when and are not to be construed as limitative. All percentages aged at elevated temperatures; they display significantly d parts are by Weight better flex-crack resistance; and they have a higher percentage of elongation and toughness at equivalent EXAMPLE XIII flexibility levels. To 60 parts of vulcanized rubber scrap particles and When compared to the vulcanized rubber compositions vulcanized rubber dust particles having a mesh size of (Table II, Examples lX-XI), these selected thermo- 50 was added 3 parts of dicumyl peroxide acting as the plastic resins were easier to process since there was no crosslinking agent. This mixture was then milled with rubber stock to be broken down beforehand and no 40 parts of an ethylene-ethyl acrylate copolymer, containvulcanization was required with its accompanying drawing 15 percent combined ethyl acrylate and having a backs of scorching and long cure cycles. In addition, melt index of 6.0, for 3 /2 minutes on a 2-roll rubber mill they displayed better tensile strength than the vulcanized at 120 C. The resulting compound was compression rubber compositions which were not reinforced With molded under 200 p.s.i. at 175 C. for 15 minutes. The carbon black and a higher percentage of elongation than properties and results of tests are set forth in Table IV. ttih;1 Scarbon black reinforced vulcanized rubber compos1- EXAMPLE XIV As was stated hereinabove, selected thermoplastic cross- The same procedure was followed as in Example XIII linkable copolymers may also be used as bonding agents except that a polyethylene having a density of 0.92 and in obtaining the reconstituted rubber product of this ina m lt ind x of s Used instead of the fithylene-ellhyl vention. In order to establish that cross-linking actually acrylate copolymer. Test results and properties are listed takes place, a standard control was compounded which is in Table IV. set forth and illustrated by Example XII below. All EXAMPLE XV percentages and parts are by weight.

The same procedure was followed as in Example XIII EXAMPLE XII except that a chlorinated polyethylene copolymer hav- To 636 parts of an ethylene-ethyl acrylate copolymer, mg a t index of nn a density and containing 15 Percent combined ethyl acrylate and haw was chlorinated to contain 20% chlorine was used 1ning a melt index of 60, were added 10 Parts of dicumyl stead of the ethlyene-ethyl acrylate copolymer. Test reperoxide, which acted as the cross-linking agent. The insuns and Propemcs are hsted m Table gredients were charged to a Banbury mill which was at a temperature of 120 C. To this composition was added EXAMPLE XVI 2542 parts of vulcanized rubber scrap particles and rub- The same procedure was followed as in Example XIII ber dust particles having a mesh size of 40. The entire except that a semi-rigid chlorinated polyethylene having batch fiuxed at C. and dropped at C. The a melt index of 0.4 and a density of 0.96 and which was total cycle time was 5.5 minutes. The compound was chlorinated to contain 20% chlorine Was used instead of then milled on a 2-roll rubber mill for 4 minutes and the ethylene-ethyl acrylate copolymer. Test results and the resulting sheeted stock was compression molded properties are listed in Table IV.

TABLE IV Example XII Example XIII Example XIV Example XV Example XVI Tensile Strength 800 1, 000 1, 150 900 1, 600 Percent Elongation 105 76 80 80 Tensile Strength at 100% Elongation 1, 000 Failed 725 Failed Ross Rubber Flex Life, Cycle Range of Initial Failures 18,000-20, 000 600,000-950, 000 180,000-250,000 1,000,000-1,600,000 60, 000-73, 000

under 200 p.s.i. at C. for 4, 8 and 15 minute curecycles. The reconstituted vulcanized rubber plaque was readily removed while still hot without pre-cooling the mold.

The resulting product was tested in the same manner as the preceding products. Similar tests were conducted with the products obtained under Examples I and X It will be noted that when thermoplastic copolymer binders were employed and were cross-linked, the strength 60 of the resulting product was materially enhanced. Furthermore, the cross-linked products display properties of improved flex-life, may be removed while still hot from a hot mold similar to vulcanized rubber and involve relatively short cure cycles. When compared to the vulcanhereinabove. These results are set forth in Table III. 65 ized rubber compositions (Table II, Examples IX-XI),

TABLE III Example XII Cured at 160 C.; Pulled Hot Example I After- Example X 3 min. at 150 C.; 20 min. at Pulled cold; cycle Cure 4 min. 8 min. 15 min. 154 0. time, 8 min.

Tensile Strength 660 775 775 750 725 Percent Elongation 125 125 110 60 Flexural Stifiness at 23 C 3, 640 3, 860 4, 360 1, 910 3, 640

Ross Rubber Flex Life, Slitted Length of crack after 25,000 flexes (100 mils/slit) mils 160 130 225 100 1 1,000

1 Complete failure.

they exhibit a higher degree of elongation with greater rigidity. Even where a low density polyethylene was cross-linked (Example XIV), the resulting product was inferior to that obtained when a thermoplastic copolymer was cross-linked since the low density polyethylene product displayed a lower percentage of elongation and significantly poorer flex-crack resistance. In general, a product closely resembling regular vulcanized rubber is readily obtainable when employing the selected copolymers having the aforementioned optimum mechanical proper ties than when other compounds are employed, as has been illustrated hereinabove.

While this invention has been described in detail and with particularity, it should be understood that changes and modifications may be made in the methods, processes, and compositions described herein without departing from the scope and spirit of the invention as contained in the appended claims.

What is claimed is:

1. A reconstituted rubber product which comprises vulcanized rubber scrap particles and vulcanized rubber dust bonded together by an ethylene polymer selected from the group consisting of interpolymers of ethylene and copolymerizable olefinically unsaturated monomers, elastomeric, chlorinated post-reacted ethylene homopolymers and elastomeric, chlorosulfonated post-reacted ethylene homopolymers, said ethylene polymer having a tensile strength of more than 500 p.s.i., a tensile elongation of more than 200 percent, and a torsional rigidity of between about 2000 psi. and 15,000 p.s.i.

2. The reconstituted rubber product of claim 1 wherein the vulcanized rubber scrap particles and vulcanized rubber dust particles are present in ratios of between about 20:1 to 0511 parts of vulcanized rubber dust particles and vulcanized rubber scrap particles to the ethylenepolymer, respectively.

3. A reconstituted rubber product which comprises vulcanized rubber scrap particles and vulcanized rubber dust having a particle size of between about 20-150 mesh bonded together by an ethylene polymer selected from the group consisting of interpolymers of ethylene and copolymerizable olefinically unsaturated monomers, elastomeric, chlorinated post-reacted ethylene homopolymers and elastomeric, chlorosulfonated post-reacted ethylene homopolymers, said ethylene polymer having a tensile strength of more than 500 p.s.i., a tensile elongation of more than 20-150 mesh bonded together with a selected ethylene polymer whose mechanical properties exhibit a tensile strength of more than 500 p.s.i., a tensile elongation of more than 200 percent, and a torsional rigidity of between about 2000 psi. and 15,000 p.s.i. and a cross-linking agent for said ethylene polymer.

4. The reconstituted rubber product of claim 3 wherein the cross-linking agent is a peroxide.

5. The reconstituted rubber product of claim 3 wherein the cross-linking agent is sulfur.

6. The reconstituted rubber product of claim 3 wherein the cross-linking agent is an isocyanate.

7. A reconstituted rubber product which comprises vulcanized rubber scrap particles and vulcanized rubber dust having a particle size of between about 20l50 mesh bonded together by an ethylene polymer selected from the group consisting of interpolymers of ethylene and copolymerizable olefinically unsaturated monomers, elastomeric, chlorinated post-reacted ethylene homopolymers and elastomeric, chlorosulfonated post-reacted ethylene homopolymers, said ethylen polymer having a tensile 12 strength of more than 500 p.s.i., a tensile elongation of more than 200 percent, and a torsional rigidity of between about 2000 p.s.i. and 15,000 p.s.i., and a plasticizer.

8. The reconstituted rubber product of claim 7 wherein the plasticizer is selected from the group of plasticizers which are highly aromatic mineral extender oils.

9. The reconstituted rubber product of claim 7 wherein the plasticizer is selected from the group of plasticizers which are naphthenic mineral extender oils.

10. A reconstituted rubber product which comprises:

(1) vulcanized rubber scrap particles and vulcanized rubber dust having a particle size of between about 20-150 mesh;

(2) an ethylene polymer selected from the group consisting of interpolymers of ethylene and copolymerizable olefinically unsaturated monomers, elastomeric, chlorinated post-reacted ethylene homopolymers and elastomeric, chlorosulfonated post-reacted ethylene homopolymers, said ethylene polymer having a tensile strength of more than 500 p.s.i., a tensile elongation of more than 200 percent, and a torsional rigidity of between about 2000 p.s.i. and 15,000 p.s.i.;

(3) a cross-linking agent for said ethylene polymer;

and

(4) a plasticizer.

11. The reconstituted rubber product of claim 10 wherein the vulcanized rubber scrap particles and vulcanized rubber dust particles are present in ratios of between about 20:1 to 0.5 :1 parts of vulcanized rubber dust particles and vulcanized rubber scrap particles to the ethylene polymer, respectively.

12. A reconstituted rubber product which comprises:

(1) vulcanized rubber scrap whose particles have a thickness of between about to A,", a width of between about A" to /3", and a length of between about to 2 /2 prior to milling;

(2) an ethylene polymer selected from the group consisting of interpolymers of ethylene and copolymerizable olefinically unsaturated monomers, elastomeric, chlorinated post-reacted ethylene homopolymers and elastomeric, chlorosulfonated post-reacted ethylene homopolymers, said ethylene polymer having a tensile strength of more than 500 p.s.i., a tensile elongation of more than 200 percent, and a torsional rigidity of between about 2000 p.s.i. and 15,000 p.s.i.

(3) a cross-linking agent for said ethylene polymer;

and

(4) a plasticizer.

13. The reconstituted rubber product of claim 12 wherein the vulcanized rubber scrap includes vulcanized rubber dust particles having a particle size of between 20-150 mesh.

References Cited UNITED STATES PATENTS 3,406,127 10/1968 Alexander 2604 2,653,914 9/1953 Elgin et al. 2602.3 3,057,390 10/ 1962 Pattison 260-2.3

MORRIS LIEBMAN, Primary Examiner R. BARON, Assistant Examiner US. or. X.R. 

